1. Field of the Invention
The invention relates to a multilayer plastic pipe.
2. Discussion of the Background
Plastic pipes of polyamide are known and are used for a variety of applications. To perform their function, the pipes have to be, inter alia, inert to the medium flowing in them and also resistant to high and low temperatures and mechanical stresses.
Single-layer pipes are not always able to fulfill the necessary requirements. For example, in the transport of aliphatic or aromatic solvents, fuels or the like, single layer pipes display considerable disadvantages, such as inadequate barrier action towards the medium, undesired dimensional changes or insufficient mechanical stressability. Reducing permeation is particularly important because the permissible emission values are being reduced ever further by legal requirements.
Attempts have been made to eliminate these disadvantages by means of multilayer pipes (DE-A 35 10 395; 37 15 251; 38 21 723; 40 01 125; 40 01 126). In practice these proposals can solve individual disadvantages, however, the overall property profile is still unsatisfactory.
FR-P 2 602 515 describes a two-layer pipe having an outer layer of polyamide 11 and an inner layer of plasticized polyvinylidene fluoride. Investigations have shown that the barrier action towards the medium flowing through is unsatisfactory. In particular, the permeation of methanol-containing fuels could not be reduced sufficiently.
The unpublished German Patent Application P 43 26 130.2 discloses thermoplastic multilayer composites of PVDF and polyamide. To achieve adhesion of the layers to one another, the PVDF contains small amounts of a polyglutarimide. However, multilayer pipes are not explicitly described.